Pavement mixture.



- ment. The fines are reduced as nearly as UNITED STATES PATENT FFEGEQWALTER S.,WILKINSON, OF BALTIMORE MARYLAND.

PAVEMENT MIXTURE.

Specification of Letters Patent.

Patented Nov. 13. 1906.

Application filed June 26,1902. Serial No. 118.288.

To all whom it may concern.-

Be it known that I, WALTER S. WILKIN- SON, a citizen of the UnitedStates, residing at Baltimore, in the State of Maryland, have inventedan Improvement in Paving or crushed stone with additional dust or fines.

If for sheet pavement, the body material is usually sand and dust orfines. The binding agent heretofore usually employed, so far as known tome, has been an asphaltic cement containing, say, from ten per cent. totwenty per cent. of residuum of petroleum or other flux mixed therewithwhile heated. The as phalts commonly employed for this cement, if usedalone, are objectionable because friable at ordinary temperatures, andit is to obviate this, so far as possible, that the fiux oil is added.It is customary to add as much flux oil as possible without renderingthe pavement unduly soft in warm weather in order to reduce, so far aspossible, the friability of the pavement in cold weather.

That pavement or composition is the best and most desirable, otherthings being equal,

wherein the body material alone is relied upon to furnish the principalresistance to the wear of trafii c. To accomplish this, all voids, sofar as possible, should be filled with stony particles rather than withfree cement, the cement serving merely as a surface film orcoatin tobind or unite every part of the surface 0 each stony particle to thesurfaces of the next adjacent stony particles, however coarse or finethe latter may be;-and the resence of voids, however minute, that arefilled with free cement constitutes an element of weakness in anybituminous pavepossible to the form of an impalpable powder or dust themore completely to fill the smallest voids in the mixture orcomposition, and such fines are usually mainly or wholly of limestone,because limestone appears to pos- 'ment, when finally sess a pronouncedaffinity or adhering caacity for bituminous cement. Limestone,urthermore, possesses a detrimental capacityviz.,'a capacity forabsorbing the residuum or other oil commonly used as a flux.

At least its flux-absorbent capacity is greater than that of any othermaterial ordinarily used for fines; and obviously this detrimentalabsorption of the fiux oil by the fines is promoted by the otherwisebeneficial proortionate increase of the amount of fines used to that ofthe cement.

In the preparation of the mixture or composition the prevailing customformerly was to dry-mix all the body material-viz., the

crushed stone or sand and all the fines-and then and while suchbodymaterial was in a state of agitation,

the same therewith to form pavement mixture or composition ready forcompression into blocks or tiles or for laying upon the roadway.

In my United States Patent No. 705,728,

dated July 29, 1903, I disclosed an improvement upon the formercustom-in the prepara tion of paving or pavement mixtures orcompositions, said improvement being based upon myldiscovery that theproportion of fines in the mixture or composition m1 ht be largelyincreased and the proportion o bitumen decreased if a considerable partof the fines be first'mixed with the cement before the, latter is addedto the remaining body material, and this fines-impregnated ceadded tosuch remalning body material, would carry said fines with It into theremotest and most minute voids in the mixture, thereby filling suchvoids with fines and cement instead of with free cement.

in quality and durability, but it is cheaper also, because less bitumenis required, =1t being restricted to its proper function-via, cementingone stony particle to another and not used as a filler for voids whichproperly should be filled with cement-coated stony particles. Whilethese advantages are great and of themselves sufficient to jusltify theintroduction of fines by the use of a finesimpregnated cement asdescribed in said patent, it is also true that the fullest possiblebenefits from the use of a fines-impregnated cement are not realizedthereby, because the increased amount of fines used and the morecomplete and thorough distribution thereof as in a usual pug-mill, to;add'the asphaltic cement thereto and mix the complete The pavement thusmade is not only superior throughout the mass increases the detrimentalabsorption by such fines of the flux oil in the cement and decreasesthepossible life of'the pavement.

I have also found by careful investigation that residuum of petroleum orother flux oil,

such as is. usually incorporated in the asphaltic cement, when exposed,as in a pavement, to the air and other elements for a term of yearsgradually deteriorates. This deterioration occurrim during atmosphericexposure I term oxi ation" for want of a better term, although it isprobable that more or less action other than strict oxidation takesplace. Whatever be the exact nature of this detrimental ,ordeteriorating action, it is a fact that it aids in the disintegrationordestruction of the pavement by rendering it more friable, and when theotherwise advantageous fines-impregnated cement is used the resultantmore thorough distribution of the cement throughout the pavement and theconsequent more complete exposure of the cement to the action of theelements tends to promotedisintegration, such as above referred to, "andthus further revents a full realization of the possible beneiitsobtainable by the use of the finesimpregnated cement.

My present invention aims to produce a pavmg or pavement mixture orcomposition out the .mass' to the most complete extent and be reduced byimpregnation therewith of the fines to the thinnest possible desirablecondition of surface coating without danger of destructive action, dueto absorption or other elimination of oil therefrom.

To eliminate the destructive oxidizing action above referred to asoccurring after the pavement is laid, my present invention comprehendsconvertin the residuum or other flux by artificial oxidation, as by theaction of air or otherwise, to a pitchy condition which is substantiallypermanently elastic and characterized by a relatively high melting-pointand non-friability at relatively low temperatures, and this conversionis effected preferably before, but it may be after, the flux soconverted is incorporated in the coment. Thus however completelysuchcement may belirestricted by fines-impregnation to a surface coatingmerely disceases tributed throughout the pavement composition no change"will occur upon exposure to the air, it having been already chan ed byair artificially brought in contact with by other suitable means beforeit was intro duced into the composition.

I have fpund, furthermore, that both the elimination of substantiallyall absorbable flux or oil, as .well as the elimination of substantiallall oxidizable elements are for convenience obtainable by one and thesame treatmentviz., the subjection of the flux to the action of asuitable agent, such as air' of the cement. Obviously it is preferableto subject the flux to the action of the converting agent prior to theformation of the ce ment, because at that time there is less volume tobe acted upon, and nothing is gained by contact of such agent with theasphalt.

In carrying out my invention I take the asphaltfor instance, Trinidadasphalt, and preferably refine the same, as by the means disclosed in mvUnited States Patent No. 512,348, dated January 9, 1894-, to realsopreferably desalify it, as by the process disclosed in my United StatesPatent No. 597,892, dated January 25, 1898. I then take any usualflux-such, for instance, as residuum of petroleum-and subject the sameto the oxidizing action of-a suitable agent in any suitable manner, asby project: ing air into or through it while heated, say, to 400Fahrenheit, the air also being preferably but not necessarily heated.The refined asphalt and the oxidized flux are then mixed in a suitablereceptacle in the presence of heat. I have found equal ortions, byweight, of Trinidad asphalt and oxidized flux to produce excellentresults. If an asphalt be used containing a larger percentage of purebitumen than Trinidad, a larger percentage of the oxidized flux couldand would be employed, for while the flux in the oxidized state atordinary temperatures possesses a less degree of liquidity thanunoxidized flux, yet when incorporated in' large quantity with theasphalt the larger proportion of the oxidized flux to the bitumen 1n theasphalt renders the resultant asphaltic cement sufficiently liquid atproper working temperature to enable it to be conveniently and properlyhandled. After having been thoroughly mixed in this manner and whilestill in a heated condition I add a suitable quantity of dust orfinely-comminuted limestone or other earthy mattersay, in theproportions. of seventy-five pounds thereof to one hundred pounds of thebituminous cementto form a fines-im regnated cement. I do not here- ;inclaim this method of introducing the fines nor, broadly, the formationof a fines-impregnated cement, as the same in the sense here used arecovered in my said Letters Patent of it or I move the water or moisturetherefrom, and I.

prior to or even subsequent to the formation i the proportions, sa of eithe United States already referred to Hav with - adding the cement,preferably gradually, to

such remaining bodymaterial while the latter is in a state of agitation,as in a usual pugmill. When the said remaining body material consists ofcrushed stone, 1 have obtained excellent results by upin thesarne in .tfifty pounds to nine iundre and fifty pounds thereof to about onehundred and fifty pounds to one hundred and forty pounds of thefines-impregnated cement. For the best results the said remaining bodymaterial should first be heated and dry-mixed in the pug-mill and thenthe heated fines-impregnated cement added thereto and mixed therewith.The resultant mixture or composition is then ready for compression foruse. if for blocks, it is compressed under heavy pressure in a mold andthe resultant compressed body quickly cooled in flowing water orotherwise to set it exteriorly to preserve its sh ape. If for sheetavements, the said mixture is laid while eated and is tamped orrolled upon the roadway.

W hen the amount of fines that may be found with the body material,together with the fines, it is possible to add to the cement and still)reserve its necessary li uidity, does not equa the Whole amount of.Lnes desired in the mixture or composition, any additional fines may beadded to and dry-mixed with the body material in usual manner.

It must be understood, of course, that the proportions, &c., hereingiven are merely b Way of example, and that the same will in a lrespects be modified, as required, by varying conditions and materialsin connection with which the work is to be performed.

An. asphaltic or bituminous cement wherein oxidized flux is usedcontains practically no 01], at least so little that it may be regardedas negligible. Consequently there is no opportunity for destruction ofthe pavement from any cause due to the presence of such oil, as by theprocess of absorption or oxidation of oil, as heretofore. This isespecially advantageous when fines-impregnated' cement, as described inmy said appli cation is used, for it enables for the first time the fullbenefit and advantage of such cement to be realized.

The use herein for the first time, as I believe, of a fines-impregnatedcement in which the asphalt has been previously desalified is alsoimportant, for this same capacity of such cement to increase the extentto which the voids are filled with cement-coated 'fines and to.restrictthe cement to its undred and and thereby correspondingly than unoxidizedflux.

proper function of a surface coating or film onl gives opportunity forthe soluble salts an rion-bituminous organic substances ordinarily.found in Trinidad asphalt (which is most largelyused for pavementpurposes) to work to the detriment of the pavemen One reason for this isthat the 'non-desalified asphalt if used in fines-impregnated cement isspread out in thinner surfacesthan if'used in the ordinary asphalticcement, and obviously the thinner the surface containing a solubleelement the more readily it is destroyed when opportunity for thesolution of such element occurs. Hence the desalified way of thefines-impregnated cement, because it eliminates this destructivetendency, benefits the pavement. While, therefore, the benefits duetothe introduction of the fines by way of the fines-impregnated cement aresufficient to justify and warrant its use in the presence of theconceded destructiveness of flux oils or of unoxidized flux or of non-desalified asphalt, used with the cement, wherein the amount of oilsv isnegligible or with converted flux or with desalified asphalt, any or allof them, the benefits are largely increased. In the same manner also theuse for the first time in a pavin or avement mixture or composition ofesal' ed asphalt and converted flux, whether or not introduced by way offinesimpregnated cement, makes it possible, as I believe, for the firsttime in the art for. both the asphalt and the flux to exert in thepavenient composition the maximum possible beneficial effects.

asphalt is of peculiar advantage when used by any or all of them, yetwhen o While the conversion of a flux oil to a permanently elasticsubstance renders the paving composition when properly constituted farmore durable, a much larger proportion of the converted than of theunoxidized flux is required to give the pavement the neces saryplasticity. Converted flux, however, is much less affected by changes intemperature Hence a much larger proportion of the converted flux may beincorporated in the cement to render the pavement more rubbery andelastic at low temperature without danger of undue softening athightemperature. In other words, oxidined or converted flux renders thepavement nihch less friable at low temperatures, while no softer at hightemperatures. While the flux after having been subjected to the actionof a converting or oxidizing agent 'is herein referred to forconvenience as oxidized flux or converted flux, it would perhaps alsoand properly be designated as pitch.

1 claim 1. The improvement in the manufacture of bituminous pavementmixture which consists in rendering a flux oil non-absorbable throughthe action of a converting agent preparing a bituminous cement by mixingasphalt therewith, adding fines thereto and thoroughly surface-coatingthe said fines with the non-absorbable flux-oil cement and then addingthe resultant mixture to a quantity of dry-mixed remaining bodymaterial.

2. That improvement in the manufacture of bituminous paving or pavementmixture or composition which consists in producin a fines-impregnatedbituminous cement y subjecting flux oil to the action of a convertingagent and thereby forming an elastic substance, mixing the resultantproduct With asphalt to form an asphaltic cement, and impregnating thesame with fines, dry-mixing the remaining body material, and then, Whilethe latter is in agitation, mixing therewith said fines-impregnatedcement.

3. The improvement in the manufacture of bituminous paving or pavementmixture or composition which consists in forming a fines impregnatedbituminous cement containing a negligible quantity, if any, of oil,impregnating said cement With such of the fines as may be added theretoWhile still preserving the necessary liquidity .ei'the cement, agitatingthe remaining hndy rnaterial and While the latter is in agitationmixingtherewith said fines-impregnated cement.

4. That improvement in the manufacture of bituminous paving or pavementmixture or composition which consists in producing a fines-impregnatedcement by converting .the flux oil to an elastic substance, mixing theresultant product with asphalt, to form an asphaltic cement, andimpregnating the same With fines, agitating the remaining WALTER s.WILKINSON.

Witnesses:

L. RABILLoN, G. C. PoUL'rNEY.

